Keyboard/mouse state for this tick — inserted as a resource by
WindowPlugin. key_pressed/mouse_pressed are edge-triggered (true
only the tick a key/button went down); key_held/mouse_held are
level-triggered (true for as long as it’s down).
Installs a runner that opens a window (via winit) and inserts
Window/Input as resources once the event loop resumes — see
[WinitApp]. Functional on native and wasm32-unknown-unknown.